Improvements in or relating to a burner module and an integrated gas burner

ABSTRACT

A burner module that can be used in combusting an air/fluid fuel flow is described. The burner module may be incorporated in an appliance. The burner module comprises a burner face comprising catalytic material for combusting the air/fluid fuel flow and a perforated screen having a plurality of micro-perforations where the perforated screen is positioned upline to the burner face to increase combustion; an integrated gas burner for connection to a pressurised fluid fuel flow where the integrated gas burner comprises a burner module and a gas train. The gas train comprises (a) an ejector for entraining air with the fluid fuel flow; and (b) a diffusor for converting the air/fluid fuel flow kinetic energy into pressure and for performing flow expansion.

FIELD

The present invention relates to an improved integrated gas burner andto cooking and heating devices including the improved integrated gasburner.

BACKGROUND

An integrated gas burner comprises a gas train and a burner module. Thegas train has a connection to a gas supply, an ejector for forming anair/fuel mixture and a diffusor or plenum for expanding the air/fuelflow which is in fluid communication with the burner module. In aradiant integrated gas burner, the burner module comprises a burner facehaving one or more surfaces which have been coated with a catalyst.

Small-power portable LPG-fuelled appliances include portable solderingirons, hair curling tongs and camping stoves. Flameless radiant-modegas-fired burners offer safety and emissions advantages over blue-flameburners and facilitate wind-resistant operation, so are sometimesspecified for small-power appliances where indoor operation isenvisaged. As flameless burners must be fully-aerated, they must besupplied with air/fuel mixture at or above the stoichiometric ratiorequired for combustion. In small-power portable gas-fuelled appliancesfuelled by butane or propane-based blends (LPG fuel), one or more largearea-ratio passive ejectors (gas-driven jet pump) are generally used toentrain, compress and mix the required fraction of combustion air withthe fuel gas. This mixture must be distributed uniformly across theentrance aperture of the radiant burner face to assure uniformcombustion with low CO emissions. Flameless burner heads may variouslybe of substantially flat, cylindrical or conical shape, are generallysized to deliver a heat flux of less than 400 kW/sq. m, and may bear acatalytic coating to promote surface combustion rather than gas-phasecombustion in a flame.

Typically, an appliance has an ejector for forming an air/fuel mixture.A packaging problem arises in expanding the high velocity air/fuel flowdischarging from the ejector to fill the entrance aperture of theradiant burner face head, whose area is typically two orders ofmagnitude greater than that of the mixing tube of the ejector, whiledelivering a uniform velocity profile.

Usually a diffusor or plenum is used to expand the air/fuel flow.Conventional faired diffusers are prohibitively long and inefficient ifused to perform a very large flow expansion. Axial-radial diffusordesigns are known, and by folding the flow path can deliver the requiredflow expansion more space-efficiently, but are susceptible to flowseparation and therefore difficult to engineer and manufacture with highpressure recovery. Ejectors can be engineered with no diffuser,discharging flow directly to a suitably sized plenum chamber whichperforms flow expansion. This is energetically inefficient however,providing a very limited pressure rise of the entrained air for theburner designer to work with, and constraining burner design.

A noise problem also can exist in certain gas-fuelled portableappliances. The expansion of the pressurised fuel jet through the mixingejector and air entrainment is a turbulent and therefore noisy process.Without some intervening muffling, jet noise can radiate from the burneraperture. Muffling is not straightforward however, as simple resistiveattenuators are undesirable due to energy losses.

Various catalytic radiant burners are known in the prior art, such asJapanese patent publication numbers JP 560200016 A, JP 557164214 A, JP55770309 A and JP 56026210 all of which suffer from one or more problemsmentioned. Radiant burners used for cooking duties are often subject toingress of liquid or particulate foreign matter due to spillages. Thisposes a risk for delicate gas train components, and for ejector nozzlesin particular, where the burner and gas train flow are generallydirected upward opposing gravity, and can cause CO emissions to exceedregulatory limits. There is a long held need in culinary serviceindustry for radiant burners which adequately address the problem ofaxial compactness without compromising reliability, cost, durability orsafety.

A further problem concerns the need to comply with emissions regulationsconcerning uncombusted gas and carbon monoxide emissions. Carbonmonoxide emissions occur due to incomplete combustion.

A way of ameliorating these problems has been sought.

SUMMARY

According to the invention there is provided a burner module, as set outin the appended claims, for use in combusting an air/fluid fuel flowwherein the burner module comprises a burner face comprising catalyticmaterial for combusting the air/fluid fuel flow and a perforated screenhaving a plurality of micro-perforations wherein the perforated screenis positioned upline to the burner face to increase combustion. It willbe appreciated that the term fluid used in the context of the presentinvention encompasses gas. The invention provides a compact burnermodule adapted to perform a large flow expansion between a gas jet inletand a burner aperture outlet, in a minimum of axial length, in a compactvolume, with minimal use of expensive catalytic surface area, while alsoproviding excellent handling qualities in use.

In one embodiment there is provided a burner module for use incombusting an air/fluid fuel flow wherein the burner module comprises aburner face comprising catalytic material for combusting the air/fluidfuel flow and a perforated screen having a plurality ofmicro-perforations and the perforated screen is positioned upline to theburner face to increase combustion, wherein the perforated screen isformed from a material having a thermal conductivity adapted to reducethermal bridging from the burner face and reflect incident heatradiation in a direction substantially perpendicular to the burner face.Suitably the perforated screen can be made from a thin material, such asa metallic foil or coated with a metallic foil.

According to the invention there is further provided an integrated gasburner for connection to a pressurised fluid fuel flow wherein theintegrated gas burner comprises a burner module and a gas train whereinthe burner module comprises a burner face comprising catalytic materialfor combusting the air/fluid fuel flow and a perforated screen having aplurality of micro-perforations wherein the perforated screen ispositioned upline to the burner face to increase combustion; and the gastrain comprises:

-   -   (a) an ejector for entraining air with the fluid fuel flow; and    -   (b) a diffusor for converting the air/fluid fuel flow kinetic        energy into pressure and for performing flow expansion.

According to the invention there is also provided a perforated screenshaped for use in an integrated burner according to the inventionwherein the screen forms a plurality of micro perforations.

According to the invention, there is further provided an appliancecomprising an integrated burner according to the invention.

The present invention provides an integrated burner having an improvedrate of combustion, effective flow metering, mixing and expansion of airand fuel flows while avoiding the noise, overheating tendencies and flowinstability of known methods of flow expansion in a gas train. As aresult of the increased combustion which gives an improved rate ofcombustion, a reduction in the amount of emissions is envisaged,specifically a reduction in the amount of uncombusted gas and carbonmonoxide produced by the burner module or integrated burner in usecompared to a known burner used in comparable conditions. Furthermore,the perforated screen minimises ingress of liquid or other foreignmatter into the gas train. This enables a compact, low costclose-coupled radiant integrated burner and gas train module to beengineered, with good durability and stability.

In some embodiments, the perforated screen may be positioned adjacent tothe burner face, for example a few gas jet diameters upline of theburner face. In some embodiments, the burner face has an aperture whichis its upline facing surface which admits the air/fluid fuel mixture. Insome embodiments, the perforated screen may be a homogenisationperforated screen which has perforations arranged to improve theuniformity of combustion across the aperture of the burner face.

In some embodiments, the integrated burner or burner module according tothe invention may comprise two perforated screens upline of the burnerface wherein the perforated screens comprise a throttling perforatedscreen and a homogenisation perforated screen wherein the homogenisationperforated screen is positioned upline and adjacent to the burner faceand the throttling perforated screen is positioned upline of thehomogenisation perforated screen; and wherein the perforations on thethrottling perforated screen are arranged to provide a predetermineddegree of aeration of the air/fuel mixture. It will be appreciated thatby setting the overall burner backpressure to passage of air/gas mixtureby selectively fitting a throttling screen of the most appropriatecombined flow area (pressure drop). The tuned backpressure can then beused to control the ratio of entrained air to driving gas flow.

In some embodiments, the perforations on the throttling perforatedscreen may be arranged to provide a flattened velocity profile of theair/fluid fuel flow perpendicular to the throttling perforated screen toprovide uniform combustion. In some embodiments, the integrated burnermay be a radiant integrated burner comprising two perforated screenswherein the throttling perforated screen provides a fully-aeratedair/fuel mixture. In some embodiments, the degree of aeration of theair/fuel mixture provided by the throttling perforated screen may be12-20 parts of air entrained with each part of fuel gas (by weight). Theadvantages of providing such a degree of aeration include that theair/fuel ratio is greater than stoichiometric and that the need forsecondary combustion is minimised such that clean burning of fuel ismore likely. In some embodiments, the perforated screen may be shaped toprovide one or more supports for the burner face. In some embodiments,the one or more perforated screen supports may have a pointed shape tominimise thermal bridging. In some embodiments, the perforated screenmay have one or more ribs to provide axial stiffness.

In some embodiments, the plurality of perforations of the perforatedscreen may be shaped to increase spill resistance and noise attenuation.It has been found that the burner module and the integrated burneraccording to the invention are noticeably quieter in use than comparableknown burner modules and integrated burners. For example noiseattenuation can be achieved using Helmholz resonators for noiseabatement (e.g. some types of auto exhaust mufflers). In the context ofthe burner module of the present invention a succession of highimpedance and low inpedence flow channels to a turbulent (noisy) fluidflow. Hence two screens and three plenums provide some noiseattenuation.

Fuel pressure-driven catalytic radiant integrated burners for LPGservice generally require a gas train with a physically long flow lengthto efficiently mix and expand separate flows of air and vaporous fuel toa larger area homogenous flow of uniform velocity. This flow lengthscales approximately with the square root of burner power. The presentinvention overcomes this problem with gas flow train length.

Gas trains which provide the required flow expansion and air/fuel mixingwith poor efficiency can make it impossible to engineer radiantintegrated burners which are free of flame-lift and light-back under alloperating conditions. This leads to a conflict between compactness andlow cost on the one hand and performance and reliability on the other.The present invention overcomes this problem. The advantages of thepresent invention include:

a. Use of one or more perforated screens having plurality ofmicro-perforations to:

-   -   i. turbulate the boundary layer of fuel and oxygen species        adsorbed onto the catalytic surfaces, thus significantly        boosting the surface combustion efficiency without need of        additional stages of mesh in the burner face to ‘scavenge’ and        combust the products of incomplete combustion;    -   ii. suppress tendency to light-back of the integrated burner due        to the close proximity of the screen plate to the burner face        and the high gas velocity in, and long aspect-ratio of the        orifices in the screen;    -   iii. protect the gas train upstream of the burner face by        filtering out and preventing ingress of liquid and particulate        solid contaminants which jeopardise the patency of small        orifices and passageways used to meter gas and air and to assure        effective air/gas mixing;    -   iv. homogenise approaching mixture velocity profile across the        profile of the burner face, improving resistance to flame lift        when cold and during catalyst light-off;    -   v. enable the use of a compact gas train having a relatively        short distance from the ejector such that there is        close-coupling of one or more ejector-mixers to the burner face,        by ensuring effective radial diffusion and mixture distribution        across the inlet aperture to the burner face such that a minimum        of axial space is required; and    -   vi. enable enhanced air/gas micro-mixing without the requiring        the use of a plenum through the turbulence-promoting action of        impacting microjets caused by flow through a perforated screen        upon the catalytic surfaces of the burner face.

In some embodiments, the perforations of the perforated screen may bechemically etched perforations. In some embodiments, the perforationsmay have a cusp. In some embodiments, the perforated screen may beformed from a metal such as aluminium or steel. In some embodiments, theperforated screen may have perforations which have uniform density anddiameter across the perforated area such that the perforated screen is ahomogenisation perforated screen such that it may bring about intensemixing of chemical species in the boundary layer adhering to a catalyticburner face. In some embodiments, the perforated screen may have athickness which is from 0.1 mm to 1 mm, for example 0.35 mm. In someembodiments, the diameter of the perforations of the perforated screenmay be from 0.1 to 0.5 mm, for example 0.25 mm. In some embodiments, theperforated screen may have a square, rectangular, curved or threedimensional shape (such as a cylindrical, spherical or cuboid shape). Insome embodiments, the perforated screen may be reflective.

In some embodiments, the perforated screen may be formed from a thinfoil having a low thermal conductivity to reduce thermal bridging fromthe burner face. In some embodiments, the thin foil may be a metallicfoil.

In some embodiments, the perforated screen may be a throttling screenand may have a plurality of perforations in a plurality of perforatedareas In some embodiments, the density (number of perforations per unitarea) and/or diameter of the perforations may be the same or differentin each of the plurality of perforated areas and may vary across eachperforated area such that the rate of flow across the plurality ofperforated areas is regulated. In some embodiments, each perforated areamay have the same or a different shape such as a triangular, square,rectangular, radial, annular, polygonal, curved, sector and/or irregularshape as may be required in order to homogenise the gas flow.

In some embodiments, the perforated screen may be formed from acorrosion-resistant malleable, dimensionally-stable metal sheetmaterial, may be capable of sustaining service temperatures in the range300-600° C. for the intended life of the integrated burner and/or may becapable of being polished to efficiently reflect infrared radiation, forexample radiation in the wavelength range of from 0.5 to 7.5 μm. In someembodiments, the perforated screen may be formed from cold-reducedaustenitic or martensitic stainless steel strip or FeCrAL alloy orsimilar alloy. It can be difficult to avoid radiation of heat from theburner face back into the plenum, causing parts to overheat especiallywhen the burner face is presented to external surfaces which reflectincident radiation efficiently. This is a particular risk in radiantcamping stoves, making safe management of burner temperature in allpossible conditions of use and the avoidance of light-back difficult toassure. The embodiment having a perforated screen which is capable ofreflecting infrared radiation overcomes these problems. This is becausethe infrared reflecting perforated screen may re-radiate radiant energyfrom the back surfaces of the burner face back out of the burner module,helping to moderate burner self-heating.

In some embodiments, the perforated screen may be manufactured by hotneedle rolling, laser-cutting, waterjet-cutting, CNC machining andchemical milling. In some embodiments, the perforated screen may beelectropolished to remove burrs. In some embodiments, the perforationsof the perforated screen may have a cusp to provide a sharp-edgedorifice to fluid flow, producing a consistent jet diameter with minimalfrictional energy losses.

In some embodiments, the perforated screen may be shaped to provide asupport for the burner face. Advantages of the perforated screen supportinclude that it provides means of stabilising large spans of alight-gauge radiant flat mesh burner face against slumping or handlingdamage by supporting the burner face from the rear. In some embodiments,the perforated screen support may have a conical shape in order tominimise any thermal bridging effect.

In some embodiments, the perforated screen may be formed from a smoothmaterial, having high reflective efficiency to IR and/or havingrelatively low heat conductivity such that much of the air/fuel fluidflow can be baffled from rearward infrared radiation from the burnerface, limiting burner temperature rise, risk of light-back, and boostingradiant efficiency. In some embodiments, the mean reflectivity of theperforated screen material to normally-incident radiation in the range0.5-7.5 μm may exceed 80%. In some embodiments, the thermal conductivityof the screen material may be less than 20 W/m·K.

In some embodiments, the gas train of the integrated burner may comprisea diffusor and/or a plenum. In some embodiments, the plenum may have across-sectional area which increases in the direction of the fluid flow.In some embodiments, the diffusor may have a cross-sectional area whichincreases in the direction of fluid flow.

In some embodiments, the gas train of the integrated burner according tothe invention may comprise an axial ejector. In some embodiments, anaxial ejector may comprise a co-axial gas injector nozzle and one ormore radial air inlets. In some embodiments, the ejector may have across-sectional area which decreases in the direction of fluid flow.

In some embodiments, the gas train may comprise a radial diffusordownline of the ejector. In some embodiments, the burner may compriseone or more disc shaped perforated screens. In some embodiments, the gastrain provides fluid communication from a gas fuel source and an airinlet to the burner module. In some embodiments, the integrated burnercomprises a fuel source, for example a gas fuel source.

In some embodiments, the gas train may comprise a folded air/fuel fluidflow such that the integrated burner is a compact integrated burner. Insome embodiments, the gas train may comprise a co-annular foldedair/fuel fluid flow. In some embodiments, a compact integrated burnermay comprise an ejector, an annular diffusor, an annular homogeniser,optionally an annular plenum and/or a cylindrical or annular burnerface. In some embodiments, a compact integrated burner may comprise oneor more radially-arranged ejectors feeding a common compact plenum. Useof a folded air/fuel fluid flow path through the compact integratedburner allows the axial length of the gas train to be collapsed andsimultaneously to provide a plenum of meaningful volume. In someembodiments, where the gas train comprises an annular diffusor connectedto an annular plenum, the annular diffusor may be shaped to provide adegree of swirl where it discharges into the annular plenum, potentiallyimproving mixing further.

In some embodiments, the burner module may comprise a crimp ring forattaching a perforated screen to the burner face. In some embodiments,the crimp ring may comprise a clip for attaching the burner module to agas train. In some embodiments, the crimp ring may be shaped to providea radial space to allow the burner module to thermally expand in use. Insome embodiments, the crimp ring may prevent slip of the air/fuelmixture past the burner module. In some embodiments, the burner modulemay comprise one or more axial spacers for providing axial separationbetween a perforation screen and the burner face or between perforationscreens. In some embodiments, the axial separator for placement betweena perforated screen and the burner face may be selected to have an axiallength which is sufficiently short to reduce the risk of light back andoverheating of the perforated screen whilst sufficiently long such thatflow from the perforated screen turbulates the burner face. A skilledperson would understand how to select a suitable axial length for suchan axial separator. The crimp ring accordingly allows an effectivecatalytic burner face to be engineered. By minimising slip past theburner module, the crimp ring enables the radiant burner face to besupplied with a flow of mixed air/gas mixture across its entranceaperture. The radial space of the crimp ring may allow the burner faceto be thermally decoupled from its mounting to avoid cold spots andallows the burner face to thermally expand and contract freely to avoiddeformation and/or low-cycle fatigue effects.

In some embodiments, the gas train may comprise an adaptor forconnection to a pressurised fluid fuel source. In some embodiments, theburner face may comprise a metal mesh, a porous ceramic monolith and/oran open-cell metal foam treated with a combustion catalyst. A suitablecombustion catalyst includes platinum (Pt), palladium (Pd), rhodium (Rh)and/or a rare earth compound. In some embodiments, the burner face mayhave a sufficient area to fully combust the required fuel to generatethe target power output. In some embodiments, the burner face may have agreater catalytic area than may be required to assure completecombustion of fuel to allow for imperfections such as incomplete air/gasmixing, non-uniform mixture velocity across the burner face, orexcessive conduction of heat away from the burner face to its mounting.

In some embodiments, the gas train may comprise an axial gas inlet. Insome embodiments, the gas train may comprise one or moreradially-arranged ejectors.

The compact gas train and radiant burner technology described here canbe used in many portable and permanent combustion applications,including heating and combustible gas purification and flaringapplications. In some embodiments, an appliance according to theinvention may be a food warming device such as a chafing dish heater, aspace heater or a stove. In some embodiments, a chafing dish heater maycomprise two nesting metal vessels and one or more integrated burnersaccording to the invention. In some embodiments, each nesting metalvessel may have a substantially flat under-surface. In some embodiments,a lower dish contains a shallow layer of water, used as a heatdistribution and coupling agent and an upper dish contains solid orliquid foodstuffs to be kept warm or cooked, and placed beneath thenested dishes are one or more integrated burners according to theinvention with a pressurised fuel supply. As the integrated burner isradiant, the appliance can be operated if necessary with minimalclearance between the burner face and the underside of the nesteddishes, as, being a fully-aerated flameless technology there arenegligible flame-quenching effects and carbon monoxide emission levelswill comply with regulatory norms under all conditions of service.

In some embodiments, a space heater may comprise a reflective surface,an integrated burner according to the invention and a pressurised fuelsource. A space heater may additionally comprise a support, anelectrical igniter and/or a handle for positioning of the reflectivesurface and/or integrated burner. In some embodiments, a stove maycomprise an integrated burner, a pressurised fuel supply, a pot support,a pot and a burner shield. The pot may be shaped such that the othercomponents can fit inside it for storage.

Designers of all types of fully-aerated integrated burners for vaporousfuels, but of radiant flameless integrated burners in particular, facethe challenges of how to expand a small diameter flow of gas into afully-aerated thoroughly mixed flow of uniform velocity entering theentrance aperture of an integrated burner. The task becomes difficultwhere space, weight, noise and cost are at a premium; where emissions ofNOx and CO must be controlled to very low levels as in indoor service;and where the only energy available for air/fuel mixing is that of thefuel pressure. The relevance of this invention is that use of thefeatures and method described eases those difficulties

The objective of this method is to provide clean-burning, quiet,long-lived ejector-mixers and radiant integrated burners, which mayoptionally be close-coupled as a module, for appliances powered by fuelvapour pressure, with minimal bulk and cost.

In some embodiments, the burner face may have a spherical, flat,cylindrical, or conical shape, particularly a flat or cylindrical shape.

To a first approximation, the packaging volume V_(b) required for aradiant integrated burner whose radiant aperture has an area A_(b) isgiven by equation (1):

V _(b) =A _(b)* L _(Tax)   (1) where

L_(T) is the path length of gas flow through the integrated burner. Thisis given by equation (2):

L _(T) =L _(e) +L _(d) +L _(p) +L _(b)  (2)

where L_(e) represents the length of the ejector, L_(d) represents thelength of the diffusor, L_(p) represents the length of the plenum (wherepresent) and L_(b) represents the length of the burner module and

L_(Tax) is the axial component of the vector sum given by equation 3:

L _(Tax) =({dot over (L)} _(e) +L _(d) +L _(p) +L _(b))  (3)

In some embodiments, the integrated burner has an arrangement whereV_(b) is minimised for a given heat input rate. Arrangements where V_(b)is minimised also tend to minimise cost. Because A_(b) is substantiallydetermined by required heat input rate, this implies minimisation ofL_(Tax) .

An expansion ratio R_(f) may be defined between the cross sectional areaof the mixing tube of the ejector (1) and the area of the exit apertureof the burner (4):

$\begin{matrix}{R_{f} = \frac{A_{B}}{A_{E}}} & (4)\end{matrix}$

R_(f) typically is in the range 50-150 for radiant burners infully-aerated ejector-driven appliances. A difficulty arises in mixingan appropriate fraction of entrained air thoroughly with the driving gasjet, then expanding the mixture flow to enter the burner entranceaperture with uniform velocity and air/gas concentration, whilesimultaneously minimising L_(T). This is because ejectors, faireddiffusers and plenum chambers need to have substantial length to operateefficiently. Gas-driven ejectors for entraining and mixing sufficientair to combust the fuel gas typically require mixing tube lengths in therange 3.5-5.5 times the tube diameter. Faired (conical diverging)diffusers are typically designed with an included angle between opposingwalls of around 5.5 degrees, while good recovery of pressure from thehigh velocity mixture discharging from the ejector requires a ratio ofdiffuser discharge area to inlet area of better than 2:1. Plenumchambers must be sufficiently large to allow flow separation or otherinstabilities at diffuser discharge to dissipate and mixture velocity tobecome homogenous. Residence time of mixture in a plenum sometimes isnecessary for sufficient molecular diffusion and micro-mixing to occurbetween phases to ensure adequate air/gas homogenisation. Given allthese considerations, L_(T) for a typical appliance tends to be large.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be illustrated with reference to the followingFigures shown in the accompanying drawings which are not intended tolimit the scope of the invention claimed:

FIG. 1A shows a schematic plan view of a first embodiment of aperforated screen according to the invention; FIG. 1B shows a schematicplan view of a second embodiment of a perforated screen according to theinvention; and FIG. 1C shows a schematic plan view of a third embodimentof a perforated screen according to the invention;

FIG. 2 shows a schematic partial cross-sectional view of a perforationof a perforated screen according to the first, second or thirdembodiment of a perforated screen according to the invention;

FIG. 3A shows a schematic cross sectional view of a first embodiment ofan integrated burner according to the present invention; and FIG. 3Bshows a schematic cross sectional view of a burner module according tothe invention as part of the integrated burner of the first embodimentof the invention;

FIG. 4A shows a computational fluid dynamics visualisation of gasdensity in moles per cubic metre of the first embodiment of anintegrated burner according to the invention in use; FIG. 4B shows acomputational fluid dynamics visualisation of gas flow in metres persecond of the first embodiment of an integrated burner according to theinvention in use; FIG. 4C shows a computational fluid dynamicsvisualisation of gas temperature in degrees Centigrade in the firstembodiment of an integrated burner according to the invention in use;and FIG. 4D shows a computational fluid dynamics visualisation showingdump diffuser diffusion effect;

FIG. 5 shows a schematic cross sectional view of a second embodiment ofan integrated burner according to the present invention;

FIG. 6 shows a schematic cross sectional view of a third embodiment ofan integrated burner according to the present invention;

FIG. 7A shows a computational fluid dynamics visualisation of gasconcentration in moles per cubic metre through the third embodiment ofan integrated burner according to the invention in use where a mixingshock is discernible close to the downline end of the radial transitionduct after which air and fuel are no longer separate phases but are wellmixed; and FIG. 7B shows a computational fluid dynamics visualisation offluid velocity in metres per second of air and vaporous fuel streamlinesof the third embodiment of an integrated burner according to theinvention in use, indicating smooth air entrainment and compressionthrough the ejector without flow separation followed by discharge intothe annular plenum;

FIG. 8 shows a schematic cross sectional view of a fourth embodiment ofan integrated burner according to the present invention, including twomixing ejectors arranged in parallel with common fuel and air inputs anda common discharge plenum;

FIG. 9 shows a schematic plan and partial cross-sectional view of thefourth embodiment of an integrated burner according to the presentinvention, but including three mixing ejectors arranged in parallel withcommon supply and delivery provisions;

FIG. 10 shows a graph depicting three alternate graded porositydistributions of the third embodiment of the perforated screen which maybe used in the first, second or fourth embodiment of an integratedburner according to the invention;

FIG. 11 shows a schematic cross-sectional view of a first embodiment ofan appliance according to the invention in the form of a chafing dishheater comprising a first embodiment of an integrated burner accordingto the invention;

FIG. 12 shows a schematic cross-sectional view of a second embodiment ofan appliance according to the invention in the form of a patio heateraccording to the invention comprising a first embodiment of anintegrated burner according to the invention; and

FIG. 13 shows a schematic partial cross-sectional and partial side viewof a second embodiment of an appliance according to the invention in theform of a camping stove according to the invention comprising a firstembodiment of an integrated burner according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

A first embodiment of a perforated screen according to the invention isgenerally indicated at 40 on FIG. 1A of the accompanying drawings.Perforated screen 40 is in the form of a metal disc 41 and has aplurality of perforations 48 in a perforated area marked 42, six radialribs 45 to stiffen the perforated screen 40 and six circular shapedsupports 44 for supporting a burner face (not shown). The perforatedscreen 40 is typically arranged in a gas train immediately upline of aburner module. The density and diameter of the perforations ishomogenous across perforated area 42. Perforated screen 40 is ahomogenisation perforated screen as its purpose includes homogenisingair/gas flow and turbulating or energising any layer of stagnant gaseswhich is coating a surface of the burner module. It has been found thatby energising such a boundary layer adhering to surfaces of the burnermodule, the reactivity of the catalysts coating those surfaces issignificantly increased.

A second embodiment of a perforated screen according to the invention isgenerally indicated at 30A on FIG. 1B of the accompanying drawings.Perforated screen 30A is in the form of a metal disc and has a pluralityof perforations 38 in a plurality of perforated areas which are marked32A,32B,32C,32D,34A,34B,34C,34D and four transverse ribs 35 to stiffenthe perforated screen 30. The density of the perforations is differentin each of the plurality of perforated areas32A,32B,32C,32D,34A,34B,34C,34D and may vary across each perforated area32A,32B,32C,32D,34A,34B,34C,34D. The purposes of the perforated screen30A are, firstly, to tune aeration of the air/fuel mixture bycontrolling back pressure in the gas train and secondly to help flattenthe velocity profile of flow across the aperture of the screen.Accordingly, perforated screen 30A is a throttling perforated screen30A. In an alternative embodiment, the perforated areas32A,32B,32C,32D,34A,34B,34C,34D may take an alternative shape such as atriangular, square, annular, polygonal, curved, sector and/or irregularshape as may be required in order to tune aeration of the air/fuelmixture and adjust the velocity profile of the flow across the apertureof the screen.

A third embodiment of a perforated screen according to the invention isgenerally indicated at 30B on FIG. 1C of the accompanying drawings.Perforated screen 30B is in the form of a metal disc 31B and has aplurality of perforations 38 in a plurality of perforated areas or zoneswhich are marked 36A,36B,36C,36D,36E,36F,36G,36H. The density of theperforations is different in each of the plurality of perforated areas36A,36B,36C,36D,36E,36F,36G,36H. Perforated areas36A,36B,36C,36D,36E,36F,36G,36H cover an outer area of the metal disc31A and have an annular shape. The purposes of the perforated screen 30Bare, firstly, to tune aeration of the air/fuel mixture by controllingback pressure in the gas train and secondly to help flatten the velocityprofile of flow across the aperture of the screen. Accordingly,perforated screen 30B is a throttling perforated screen 30B. In analternative embodiment, the perforated areas36A,36B,36C,36D,36E,36F,36G,36H may take an alternative shape such as atriangular, square, polygonal, curved, sector and/or irregular shape asmay be required in order to homogenise the gas flow. In an alternativeembodiment, the diameter of the perforations may vary across theplurality of perforated areas 36A,36B,36C,36D,36E,36F,36G,36H. In analternative embodiment, the density and/or the diameter of theperforations may vary across each perforated area36A,36B,36C,36D,36E,36F,36G,36H.

The perforations 38,48 in the perforated screens 30A,30B,40 have a cusp39,49 which narrows the radius of the perforation 38,48 by an amount37,47 as shown in partial cross-section in FIG. 2. Cusp 39,49 isbelieved to improve the performance of the perforated screen 30A,30B,40as it allows perforation 38,48 to perform as a nozzle. Metal disc has athickness 33,43 which is about 0.25 mm. The perforations 38,48 have adiameter of about 0.35 mm. In an alternative embodiment, the thickness43 may be from 0.1 mm to 1 mm. Generally speaking, the diameter ofperforations 38,48 may be greater than thickness 43 for ease ofmanufacture. In an alternative embodiment, the diameter of theperforations 48 may be from 0.1 to 0.5 mm. In an alternative embodiment,perforated screen 40 may have a different shape such as a square,rectangular, curved or three dimensional shape (such as a cylindrical,spherical or cuboid shape).

The perforated screens 30,40 have a hydraulic diameter which for eachperforated screen 30,40 is the sum of the diameters of all of theirperforations 38,48. The hydraulic diameter determines the back pressureof the throttling screen 30 and thereby the degree of aeration of anair/fluid fuel flow from the gas train may be selected by setting thehydraulic diameter by the appropriate choice of the number of theperforations 38,48 and their diameters.

Suitable perforated screens 30A,30B,40 are preferably made from acorrosion-resistant malleable, dimensionally-stable metal sheetmaterial, capable of sustaining service temperatures in the range300-600° C. for the intended life of the burner 100,200,300,400, andcapable of being polished to efficiently reflect radiation in thewavelength range 0.5-7.5 μm. Cold-reduced austenitic or martensiticstainless steel strip or FeCr alloy are suitable materials. The size ofthe required perforations depends in part upon the geometry of theburner 100,200,300,400, for example on the clearance between theperforated screen 30A,30B,40 and the upstream surfaces of a burner face150,250,350,450. A perforated screen 30A,30B,40 having perforations38,48 having a smaller diameter has improved noise attenuation and spillresistance as ingress by solid or liquid matter into the gas train orburner module is reduced.

The density of perforations 38,48 can either be fixed or can be variedacross the surface of the screen to flatten the velocity profile ofmixture entering the burner face 150,250,350,450. FIG. 1C shows anexample of a perforated screen 30B for a flat circular burner. Thesurface has been divided into annular zones36A,36B,36C,36D,36E,36F,36G,36H which all bear the same size of hole,but the hole density can easily be varied by increasing or decreasingthe hole count monotonically in each zone to achieve a ‘flat’ velocityprofile across the area of the burner face, i.e.

$\frac{dv}{dA} = 0.$

FIG. 10 depicts three alternate graded porosity distributions for thescreen of FIG. 1C obtained in this way. Overall porosity is given by theratio of total hole area to the burner entrance aperture, and canconveniently be used to adjust the mixture strength of the burner100,200,300,400.

The perforated screens 30A,30B,40 may be manufactured by a number ofmethods, of which the more convenient include hot needle roller,laser-cutting, waterjet-cutting, CNC machining and chemical milling. Forthe first four methods, improved tolerances and reduced costs resultwhere sheet material is laminated together during machining and clampedbetween thicker plates. On completion, screens may be electropolished toremove burrs. The preferred method of manufacture is chemical milling ofthe sheet material from both sides, with accurate mutual registration ofa lithographic mask on each side. According to this process, the minimumhole size that is possible with high yield is given by the materialthickness used. Referring to FIG. 2, the resulting profile of the etchedperforation 38,48 will not have parallel walls but will have a reduceddiameter cusp 39,49 approximately halfway down the bore. This can beadvantageous in that it behaves as a sharp-edged orifice to fluid flow,producing consistent jet diameter with minimal frictional energy losses.Chemical milling can be conveniently coupled with electropolishing toremove sharp edges and improve the reflectivity of the burner-facingsurface.

A first embodiment of an integrated burner according to the invention isindicated generally at 100 on FIGS. 3A and 3B of the accompanyingdrawings. Integrated burner 100 comprises a gas jet-drivenair-aspirating ejector 110, a radial diffusor of elliptical wall profile120, a disc shaped throttling screen 130 and a burner module indicatedgenerally at 159 which comprises a homogenisation screen 140, a crimpring 155 and a burner face 150. Ejector 110 has a co-axial primarynozzle 112, two radial air inlets 114 and an ejector secondary nozzle116. The primary nozzle and two radial air inlets 114 provide inlets forthe ejector secondary nozzle 116. Secondary nozzle 116 of ejector 110discharges to a mixing tube 118 which discharges to a radial diffusor120. Diffusor 120 has a cross-sectional area which broadens from narrowtube 118 to be substantially the same as that A_(B) of the burner face150. Diffusor 120 houses the throttling screen 130 and the burner module159. Diffusor 120 has a lower lip 124 for supporting the throttlingscreen 130, an axial spacer 126 for supporting the burner module 159 andan upper lip 122 for securing the burner module 159.

Burner module 159 comprises the burner face 150, the homogenisationscreen 140 and the crimp ring 155. Crimp ring 155 secures thehomogenisation screen 140 to the burner face 150. Crimp ring 155 has alower clip 158 for engagement with the homogenisation screen 140 and anupper clip 156 for securing burner face 150. Crimp ring 155 minimisesthe risk of air/fuel mixture bypassing the burner face 150.

The throttling screen 130 is supported by lower lip 124 of the diffusor120. Axial spacer 126 is placed on top of throttling screen 130 to spaceit from the homogenisation screen 140 of the burner module 159. Burnermodule 159 is placed on axial spacer 126 and is secured by upper lip 122of the diffusor 120. In an alternative embodiment, the burner module 159may comprise the homogenisation screen 140. In a further alternativeembodiment, the crimp ring 155 may comprise a clip for engaging with thediffusor 120.

Throttling screen 130 may be a perforated screen 30A according to thesecond embodiment of the invention as shown in FIG. 1B, havingperforations 138. Homogenisation screen 140 may be a perforated screen40 according to the first embodiment of the invention shown in FIG. 1A,having perforations 148. Homogenisation screen 140 is shaped to formthree supports 144 for burner face 150 to prevent burner face 150 fromsagging, to improve durability of the burner face 150 and to allow awider burner aperture (A_(B)). Support 144 has a pointed shaped tominimise thermal bridging between the homogenisation screen 140 and theburner face 150. Throttling screen 130 and homogenisation screen 140 areseparated from each other by an annular spacer 153. Burner face 150 isformed from a metal mesh which is at least partially coated with acatalytic material to ensure substantially flameless combustion of agas/air mixture. Upper clip 156 of the crimp ring 155 is shaped suchthat a radial space 152 is provided to allow for thermal expansion ofthe burner face 150 in use. Primary nozzle 112 has an adaptor (notshown) for connection to a pressurised fluid fuel source. Ejector 110has an axial length which is indicated at L_(E). Diffusor 120 has anaxial length which is indicated as the sum of L_(D) and L_(P). Burnerface 150 has an axial length L_(B). The integrated burner 100 has anoverall axial length L_(Tax) which is indicated as being the vector sumof L_(E), L_(D), L_(p) and L_(B). In an alternative embodiment, theremay be one or more air inlets 114 and/or one or more supports 144 forburner face 150

In the first embodiment of the invention, Σ(L_(d)+L_(p)) is minimised byuse of the radial diffuser 120 and substantial elimination of a plenumupline of the burner face 150. This is achieved by addition of theperforated screens 130,140 which are formed from a thin heat resistantmaterial. The upline screen 130 acts as a semi-permeable boundary forthe radial diffuser 120, ensuring high velocity mixture discharging theejector 110 negotiates the axial to radial direction change withacceptable energy losses and without severe flow separation, while alsoenabling the flow to distribute across its aperture, permeate, andprogress towards the burner face 150. The axial to radial directionchange is required because the aperture of the burner face 150 isgreater than that of the mixing tube 118. The downline screen 140 behindthe burner face 150 acts to further homogenise the velocity distributionof the mixture flow and to reflect radiation emitted by the burner face150 back out of the burner face 150. Flow passage through each screen130,140 is accompanied by considerable microturbulence due to jet actionthrough the perforations 138,148. In this way, the flow length of aconventional plenum can be greatly shortened, while the use of a radialdiffuser 120 with semi-porous boundary wall formed by screens 130,140enables flow expansion in a very short axial length. Quality of air/gasmixing over that delivered by the ejector mixing tube is improved due tothe micromixing effects of jetting through the perforations 138,148. Byfabricating the screens 130,140 from thin smooth material with highreflective efficiency to IR but relatively low heat conductivity, thegas train can be baffled from infrared radiation radiated from the rearof the burner face, limiting burner temperature rise, hence reducingrisk of light-back and boosting radiant efficiency.

A further benefit of the use of thin perforated screens 130,140 in theburner 100 according to the first embodiment of the invention isrelevant to cooking applications, where burners 100 are generallyinverted and stationed below cooking vessels. The small diameter of theperforations 138,148—typically of the same order as the thickness of thescreen material—affords some protection to the gas train from liquid andparticulate ingress via the burner face 150.

A yet further benefit of the use of at least one thin perforated screen130,140 stationed a few microjet diameters upstream of the rear of theburner face 150, is the ability to boost mass transport rate of reactantmolecules to a catalytically-coated burner face 150 through the effectsof jet impingement. The high levels of turbulence in jet impingement ofa gas mixture onto catalytic surfaces thins and turbulates the boundarylayer of reactants and products of combustion adhering to the surfaces.This decreases the catalytic area that would otherwise be required tocombust a given massflow of mixture to a given standard of completeness.

Computational fluid dynamics (CFD) visualisations of the burneraccording to the first embodiment of the invention are shown in FIGS.4A, 4B, 4C and 4D. FIG. 4A depicts a propane/butane gas jet at 280kiloPascals gauge (dark grey at bottom LHS) mixing with ambient air(dark grey at left). Blended air/gas passes from the radial diffuser 120through two perforated screens 130,140 and through the flat catalyticburner face 150 and is discharged to atmosphere. Combined screens andburner resistance of 50 Pascals was assumed. As the flow progresses downthe mixing tube 118 and jet breakup occurs, momentum is transferred tothe entrained air. Shortly after the entry to the axial-radialtransition at the inlet to the radial diffuser 120, the streamlines andvelocities in FIG. 4B clearly indicate a powerful toroidal vortex, whichin FIG. 4A appears to homogenise a partially-mixed air/gas flowdischarging from the ejector. Also clearly visible in FIG. 4B is thehomogenising effect of the screens 130,140 on velocity profile acrossthe burner face 150. Also visible is the jetting effect of theperforations 148 in the screen 140 closest the burner face 150 onto thecatalytic surfaces. FIG. 4C indicates the effectiveness of theperforated screens 130,140 in baffling much of the rearward-emittedradiation from the burner face 150 from affecting upstream mixturetemperature, reducing risk of lightback. FIG. 4D indicates theeffectiveness of dump diffuser diffusion effect 119.

A second embodiment of an integrated burner according to the inventionis indicated generally at 200 on FIG. 5 of the accompanying drawings.Integrated burner 200 comprises a gas jet-driven air-aspirating ejector210, an annular diffusor 220, an annular plenum 225, a cylindricalhomogenisation screen 240 and an outer cylindrical burner face 250.Ejector 210 has a co-axial primary nozzle 212, two radial air inlets 214and an ejector secondary nozzle 216. The primary nozzle 212 and airinlets 214 provide inlets for the ejector secondary nozzle 216.Secondary nozzle 216 discharges to a mixing tube 218 which dischargesinto annular diffusor 220. Annular duct 219 turns fluid flow radiallyand then axially to enter annular diffusor 220. Fluid flow from theannular diffusor 220 is turned radially by one or more radial outlets221 to enter plenum 225 and is directed towards the burner face 250 viacylindrical homogenisation screen 240. Homogenisation screen 240 may bea perforated screen 40 according to the first embodiment of theinvention shown in FIG. 1A except that it has a cylindrical shape.Burner face 250 may be formed from a metal mesh which is at leastpartially coated with a catalytic material to ensure substantiallyflameless combustion of a gas/air mixture. Primary nozzle 212 has anadaptor (not shown) for connection to a pressurised fluid fuel source.

The integrated burner 200 according to the invention accordingly has aco-annular arrangement of ejector 210, diffuser 220 and plenum 225 whichfolds these three elements very efficiently via two flow reversalsprovided by radial tube 219 and radial outlet 221 from the diffusor 220.This minimises Σ(L _(e)+L _(d)) and consequently L_(Tax) . The foldedgas train is used to feed a radially-firing cylindrical burner face 250.Flow from a conventional central jet ejector 210 is turned firstradially then axially into an annular diffuser 220, before finally beingturned radially again and discharged into an annular plenum 225. Flowentry into the plenum 225 can have tangential swirl imparted.

A single cylindrical perforated screen 240 is added in close proximityto the inlet surfaces of the burner face 250 to turbulate the catalyticsurfaces (not shown) of the burner face 250 and acts as a radiationbaffle. The co-annular ejector-diffuser 210,220 arrangement providesexcellent mixing of air/gas as is clear from the CFD simulations ofFIGS. 7A and 7B and a good degree of flow expansion. A second perforatedscreen for improving flow uniformity and mixing quality may beunnecessary.

A third embodiment of an integrated burner according to the invention isindicated generally at 300 on FIG. 6 of the accompanying drawings.Integrated burner 300 comprises a gas jet-driven air-aspirating ejector310, an annular diffusor 320, an annular plenum 325, an annularhomogenisation screen 340 and an annular burner face 350. Ejector 310has a primary nozzle 312 for gas injection, two radial air inlets 314and an ejector secondary nozzle 316. Primary nozzle 312 and air inlets314 are provide inlets for ejector secondary nozzle 316. Secondarynozzle 316 of ejector 310 discharges into mixing tube 318 whichdischarges into diffusor 320. Annular duct 319 turns fluid flow radiallyand then axially to enter annular diffusor 320. Fluid flow from theannular diffusor 320 is turned radially by one or more radial outlets321 to enter plenum 325 and is directed towards the burner face 350 viaannular metering screen 330 and annular homogenisation screen 340.Homogenisation screen 340 may be a perforated screen 40 according to thefirst embodiment of the invention shown in FIG. 1A except that it has anannular shape. The integrated burner 300 according to a third embodimentof the invention provides a substantially flat burner face variant ofthe integrated burner 200 according to the second embodiment of theinvention depicted in FIG. 5. Burner face 350 is formed from a metalmesh which is at least partially coated with a catalytic material toensure substantially flameless combustion of a gas/air mixture. Primarynozzle 312 has an adaptor (not shown) for connection to a pressurisedfluid fuel source.

Computational fluid dynamics (CFD) visualisations of the integratedburner 300 according to the third embodiment of the invention are shownin FIGS. 7A and 7B. FIG. 7A depicts gas concentration in moles per cubicmetre of a propane/butane gas jet at 280 kiloPascals gauge (dark grey attop LHS) mixing with ambient air (dark grey at left). Blended air/gasdischarges from the annular flat surface at the right hand end of theplenum 325 to an assumed perforated screen and burner face resistance of50 Pascals. As the flow progresses down the ejector's mixing tube 318and jet breakup occurs, momentum is transferred to the entrained air.Part-way around the flow-reversing axial-radial-axial duct 319 on theRHS, evidence of a mixing ‘shock’ can be seen, before entry into theannular diffuser 320. Note that the flow leaving the mixing tube issubsonic and remains so throughout the annular duct 319. Therefore thisrather sudden mixing does not involve a true shock wave phenomenon. Itis believed that it is associated with fluid vorticity caused by thesharp direction change of the flow. By the time the mixture isdischarged into the plenum 325, it has been thoroughly mixed (no visiblestratification).

FIG. 7B depicts flow velocity in metres per second and streamlines. Theeffectiveness of the lengthy annular diffuser in decelerating the flowvelocity is apparent, as is the good control of flow separationthroughout the gas train which is often difficult to achieve in annularducts. The mass ratio of entrained air to gas for this CFD case was20.7:1, equivalent to approximately 25% excess air for a typicalLPG-type fuel. This simulation indicates the outstandingly goodcombination of mixing effectiveness, high air entrainment and verycompact dimensions possible using gas trains folded in this way.

A fourth embodiment of an integrated burner according to the inventionis indicated generally at 400 on FIGS. 8 and 9 of the accompanyingdrawings. Integrated burner 400 comprises an axial gas inlet 405, threeradially-arranged gas/air ejectors 410A,410B,410B, three axial diffusors420A,420B,420C, an annular plenum 425, an annular homogenisation screen440 and an annular burner face 450. The ejectors 410A,410B,410C eachhave a primary nozzle 412A,412B,412C for gas injection, an axial airinlet 414A,414B,414C and a secondary nozzle 416A,416B,416C. Primarynozzle 412A,412B,412C for gas injection and axial air inlet414A,414B,414C provide inlets for the secondary nozzle 416A,416B,416C.Secondary nozzles 416A,416B,416C of ejectors 410 lead toradially-arranged mixing tubes 418A,418B,418C which discharge intodiffusing bends 420A,420B,420C. Fluid flow discharging axially from thediffusing bend 420A,420B,420C exits into plenum 425 and is directedtowards annular burner face 450 via homogenisation screen 440.Homogenisation screen 440 may be a perforated screen 40 according to thefirst embodiment of the invention shown in FIG. 1A except that it has anannular shape. Burner face 450 may be formed from a metal mesh which isat least partially coated with a catalytic material to ensuresubstantially flameless combustion of a gas/air mixture. Primary nozzles412A,412B,412C have an adaptor (not shown) for connection to apressurised fluid fuel source.

The fourth embodiment of the integrated burner according to theinvention shown in FIGS. 9 and 10 illustrates the concept ofsegmentation of a single large ejector into multiple radially oraxially-arranged smaller identical ejectors fed by a common gas supply,with single shared plenum and burner face. In an alternative embodiment,there may be more or less than three ejectors and diffusors, forexample, the gas train may have two, four or five ejectors anddiffusors.

In the integrated burner 400 according to the fourth embodiment of theinvention, Σ(L_(e)+L_(d)) is minimised. A diffusing duct 420A,420B,420Cincorporating a 90 degree bend is provided at the discharge end of eachejector 410A,410B,410C. This gas train arrangement can be packagedefficiently with radial-firing or axial-firing burner faces 450, usingat least one perforated screen 440 to homogenise flow distribution intothe burner face 450 and to turbulate catalytic surfaces.

In an alternative embodiment, the burner face 150,250,350,450 may be acatalytic radiant burner head. In an alternative embodiment, the burnerface 150,250,350,450 may comprise a porous ceramic monolith or open-cellmetal foam treated with a combustion catalyst such as platinum (Pt),palladium (Pd), rhodium (Rh) and/or a rare earth compound. Burner face150,250,350,450 has a sufficient area to fully combust the required fuelto generate the target power output. In practice, greater catalytic areamay be required to assure complete combustion of fuel in the face ofimperfections such as incomplete air/gas mixing, non-uniform mixturevelocity across the burner face 150,250,350,450, or excessive conductionof heat away from the burner face 150,250,350,450 to its mounting means.

In some applications such as flat burner types, it is advantageous toprop the burner face at additional points on its aperture in addition toproviding continuous edge support. This improves burner face durabilityin the face of rough handling of a portable gas appliance, for example.Malleable screen materials can easily have bumps formed into themthrough pressing, after perforation. By minimising the thickness of thescreen material and favouring the use of materials of low conductivity,it is possible to provide support bumps at one or more points across theaperture which contact and stabilise the upstream side of the radiantburner face, while minimising thermal bridging to the burner supportstructure.

Radiant burner faces require mounting methods that minimise heat lossesat the support points, minimise the degree of ‘slip’ or bypassing ofmixture around the burner perimeter, while enabling substantial thermalexpansion and contraction of the burner face without restraint. Hightemperature gasketing materials of needled quartz fibre are suitable.

The compact gas train and radiant burner technology described here canbe used in many portable and permanent combustion applications,including heating and combustible gas purification and flaringapplications. Three specific examples of suitable appliances areprovided in FIGS. 11, 12 and 13. FIG. 11 depicts a first embodiment ofan appliance according to the invention which is indicated generally at60. Appliance 60 is in the form of a well-known food warming or cookingdevice. A chafing dish 63,64 is provided, consisting of two nestingmetal vessels 63,64, with substantially flat under-surfaces. The lowervessel 63 contains a shallow layer of water 62, used as a heatdistribution and coupling agent. The upper dish contains solid or liquidfoodstuffs 65 to be kept warm or cooked. Placed beneath the nesteddishes are one or more integrated burners 100 each connected to aLPG-fuel container 107. As the integrated burner is radiant, theappliance 60 can be operated if necessary with minimal clearance betweenthe burner face and the underside of the nested dishes, as, being afully-aerated flameless technology there are negligible flame-quenchingeffects and carbon monoxide emission levels will comply with regulatorynorms under all conditions of service.

FIG. 12 schematically depicts a second embodiment of an applianceaccording to the invention which is indicated generally at 70. Appliance70 is in the form of space heating device for indoor or outdoor use,employing a radiant integrated burner 100 adapted to have a sphericalburner face 150. In this case, the spherical burner face 150 is placed ashort distance inside the focal point of a substantially parabolicreflector 72. Heat from the integrated burner 100 is reflected offparabolic reflector 72 as illustrated by beams 77. The integrated burneris both supported and fuelled via a tubular support 74 mounted coaxiallywith the reflector 72. A compact gas supply 107 is located behind, andis baffled by, the reflector 72 from direct radiation. Convenient burnerpower control can be provided via a projecting handle 76 which isrotatable about the reflector axis and incorporating a button control(not shown) to operate an electrical igniter (not shown). The handle 76may additionally be used to adjust the pose of the reflector 72 in tipand tilt. Optionally, the intra-focal distance of the centre ofcurvature of the burner face 150 may be adjusted via the projectinghandle 76 or by other means, enabling beam divergence to be adjusted.The reflector 72 and integrated burner 100 may be pole or wall-mountedand positioned for indoor or outdoor comfort heating, accelerated dryingor curing of coatings or composites and other purposes.

There are many advantages of applying this technology in thisapplication. A flameless radiant integrated burner has a better-definedobject shape than a blue-flame burner, while a truncated sphericalprofile is optimal for projecting a uniform heat flux on the imageplane. Radiant burners, being fully-aerated, are not susceptible to sootaccumulation on the reflective optics over time. The low mass of thecompact folded gas train embodiments disclosed here enable the suspendedmass to be minimised to the benefit of safety and stability, while themass of embodied materials and therefore the cost of the integratedburner is very low.

FIG. 13 depicts in half-section a third embodiment of an applianceaccording to the invention which is indicated generally at 80. Appliance80 is in the form of a portable single-burner LPG-fuelled stove forcamping and the like. Stove 80 comprises a pot 82, a pot support 86, aburner shield 84, an integrated burner 300 according to the thirdembodiment of the invention and fuel supply 307. The pot support 86, potsupport 86, burner shield 84, integrated burner 300 and fuel supply 307nest into the pot 82 for compact storage. The burner face 350, of outerdiameter approximately 90 mm, combusts approximately 2 kW of gas,measured by heat input rate, equivalent to a heat flux of 320 kW/sq·mapproximately. Burner face temperature is approximately 820-900° C.depending on the reflectivity of the under surface of the pot 82. Astepped substantially-conical radiation reflector with air induction andexhaust holes doubles as a pot support 86 and as windproofing screen 84.Exhaust gases are discharged through perforations around the perimeterof the radiation reflector (not shown) while infrared radiation isconcentrated within the cavity formed between perforated screen,underside of the pan, and the stepped radiation reflector.

The advantage of applying the technology in this application is thesuperior packaging efficiency, reduced weight, improved stability andlower cost of this stove when compared with state of the art stovesusing other technology. This is achieved without sacrificing othercontemporary performance features of modern LPG stove.

In the specification the terms “comprise, comprises, comprised andcomprising” or any variation thereof and the terms include, includes,included and including” or any variation thereof are considered to betotally interchangeable and they should all be afforded the widestpossible interpretation and vice versa.

The invention is not limited to the embodiments hereinbefore describedbut may be varied in both construction and detail.

1. A burner module for use in combusting an air/fluid fuel flow whereinthe burner module comprises a burner face comprising catalytic materialfor combusting the air/fluid fuel flow and a perforated screen having aplurality of micro-perforations and the perforated screen is positionedupline to the burner face to increase combustion, wherein the perforatedscreen is formed from a material having a thermal conductivity adaptedto reduce thermal bridging from the burner face and reflect incidentheat radiation in a direction substantially perpendicular to the burnerface.
 2. A burner module as defined in claim 1 wherein the module isconfigured to cooperate with a gas train to deliver air/fluid fuel fromat least one ejector.
 3. A burner module as defined in claim 2 whereinthe at least one ejector is closely coupled to the burner face via thegas train such that minimum axial space is required in use andpositioned to provide a radial diffusion and mixture distribution to theburner face.
 4. A burner module as defined in claim 3 wherein the burneris a radiant flameless burner configured to permit a minimal clearancebetween the burner face and a culinary vessel while ensuring maximumcombustion of fuel during use.
 5. A burner module as defined in claim 3comprising a step positioned at an inlet to a radial diffuser configuredto promote formation of a stable toroidal vortex to improve diffuserefficiency.
 6. A burner module as defined in any one of the precedingclaims which comprises at least two perforated screens upline of theburner face wherein the perforated screens comprise a throttlingperforated screen and a homogenisation perforated screen wherein theperforations on the throttling perforated screen are selected to providea predetermined degree of aeration of the air/fuel mixture; and theperforations on the throttling perforated screen are arranged to providea flattened velocity profile of the air/fluid fuel flow perpendicular tothe throttling perforated screen to provide uniform combustion.
 7. Aburner module as defined in claim 6 wherein the homogenisationperforated screen is positioned upline and adjacent to the burner faceand the throttling perforated screen is positioned upline of thehomogenisation perforated screen
 8. A burner module as defined in claim6 or claim 7 which is a radiant burner module comprising two perforatedscreens wherein the throttling perforated screen is configured toprovide a fully-aerated air/fuel mixture.
 9. A burner module as definedin any one of claims 6 to 8 wherein the degree of aeration of theair/fuel mixture provided by the throttling perforated screen is 12-24parts of air entrained with each part of fuel gas by weight.
 10. Aburner module as defined in any one of the preceding claims wherein theplurality of perforations of the one or more perforated screens areshaped to increase spill resistance and/or noise attenuation.
 11. Aburner module as defined in claim 10 wherein the perforations comprisean area of at least 15% of the perforated screen surface area.
 12. Aburner module as defined in any one of the preceding claims wherein theperforations have a cusp.
 13. A burner module as defined in any one ofthe preceding claims wherein the perforated screen comprises a foilmaterial or a metallic foil.
 14. A burner module as defined in any oneof the preceding claims wherein the perforated screen is polished toreduce heat transfer to the gas train and consequent generation oftemperatures at a surface confining the flow of air/fuel mixture whichare high enough to initiate light-back.
 15. A burner module as definedin any one of the preceding claims wherein the perforated screen isshaped to provide one or more supports for the burner face.
 16. A burnermodule as defined in claim 15 wherein the one or more perforated screensupports have a pointed shape to minimise thermal bridging.
 17. A burnermodule as defined in any one of the preceding claims wherein theperforated screen has one or more ribs to provide axial stiffness.
 18. Aburner module as defined in any one of the preceding claims whichcomprises a crimp ring for attaching the burner module to a gas train.19. A burner module as defined in claim 18 wherein the crimp ring isdimensioned to provide a radial space to allow the burner module tothermally expand and contract freely in use.
 20. A burner module asdefined in claim 18 wherein the crimp ring comprises an axial spacer forproviding axial separation between the burner face and perforated screenwherein the axial spacer has an axial length which is dimensioned toreduce risk of light back.
 21. A burner module as hereinbefore describedand/or illustrated with reference to the Figures of the accompanyingdrawings.
 22. An integrated gas burner for connection to a pressurisedfluid fuel flow wherein the integrated gas burner comprises a burnermodule as defined in any one of claims 1 to 21 and the gas train whereinthe gas train comprises: a. an ejector for entraining air with the fluidfuel flow; and b. a diffusor for converting the air/fluid fuel flowkinetic energy into pressure and for performing flow expansion.
 23. Anintegrated burner as defined in claim 20 wherein the integrated burneris a compact integrated burner having a folded gas train.
 24. Anintegrated burner as defined in claim 23 wherein the gas train comprisesa co-annular folded gas train.
 25. An integrated burner as defined inclaim 23 wherein the folded gas train has a reduced axial length.
 26. Anintegrated burner as defined in any one of claims 22 to 25 whichcomprises an additional perforated screen having a plurality ofmicro-perforations; preferably the perforated screen is as defined inany one of claims 2 to
 17. 27. An integrated burner substantially ashereinbefore described and/or illustrated with reference to one or moreof the Figures of the accompanying drawings.
 28. An appliance comprisingan integrated burner as defined in any one of claims 22 to 27;preferably the appliance is: a) a chafing dish heater comprising twonesting metal vessels and one or more integrated burner; b) a spaceheater comprising a reflective surface, one or more integrated burnersand a pressurised fuel source; preferably the space heater additionallycomprises a support, an electrical igniter and/or a handle forpositioning of the reflective surface; or c) a stove comprising anintegrated burner, a pressurised fuel supply, a pot support, a pot and aburner shield; preferably the pot is shaped such that the othercomponents can fit inside it for storage.
 29. An appliance substantiallyas hereinbefore described and/or illustrated with reference to one ormore of the Figures of the accompanying drawings.